U.S. patent application number 12/112712 was filed with the patent office on 2008-08-28 for multi-segment modular stent and methods for manufacturing stents.
Invention is credited to Eyal Morag, Ophir Perelson, Dmitry J. Rabkin.
Application Number | 20080208319 12/112712 |
Document ID | / |
Family ID | 28041620 |
Filed Date | 2008-08-28 |
United States Patent
Application |
20080208319 |
Kind Code |
A1 |
Rabkin; Dmitry J. ; et
al. |
August 28, 2008 |
Multi-Segment Modular Stent And Methods For Manufacturing
Stents
Abstract
A modular stent comprises at least one stent module including an
intermediate segment consisting of one of either a closed-cell
segment or a Z-segment and a pair of end segments connected to
respective longitudinal ends of said intermediate segment, each end
segment consisting of the other of said closed-cell segment or
Z-segment, each closed-cell segment consisting solely of at least
one annular closed-cell ring and each Z-segment consisting solely
of at least one annular Z-ring. A method of manufacturing a stent
form a small diameter tube includes laser-cutting the small
diameter tube to define a plurality of longitudinally adjacent
Z-rings, providing interconnector portions of said tube integrally
joining facing aligned or offset Z-rings, expanding the small
diameter tube, and removing predetermined interconnector portions
from the expanded tube to provide the predetermined desired
arrangement of interconnected closed-cell rings and Z-rings.
Inventors: |
Rabkin; Dmitry J.;
(Framingham, MA) ; Morag; Eyal; (East Hampton,
MA) ; Perelson; Ophir; (Beverly Hills, CA) |
Correspondence
Address: |
WOLF, BLOCK, SHORR AND SOLIS-COHEN LLP
250 PARK AVENUE, 10TH FLOOR
NEW YORK
NY
10177
US
|
Family ID: |
28041620 |
Appl. No.: |
12/112712 |
Filed: |
April 30, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10333600 |
Jan 21, 2003 |
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PCT/US02/38456 |
Dec 3, 2002 |
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12112712 |
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60337060 |
Dec 3, 2001 |
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Current U.S.
Class: |
623/1.16 ;
623/1.18; 623/1.34 |
Current CPC
Class: |
A61F 2002/91575
20130101; A61F 2002/91558 20130101; A61F 2230/0013 20130101; A61F
2/915 20130101; A61F 2/91 20130101; A61F 2002/91566 20130101; A61F
2230/0054 20130101 |
Class at
Publication: |
623/1.16 ;
623/1.34; 623/1.18 |
International
Class: |
A61F 2/86 20060101
A61F002/86; A61F 2/94 20060101 A61F002/94 |
Claims
1. A modular stent having an unexpanded configuration and an
expanded tubular configuration, said stent comprising at least one
pair of modules, one of said pair of stent modules comprising a
first Type A module including, an intermediate segment consisting
of a Z-segment; a pair of end segments connected to respective
longitudinal ends of said intermediate segment, each end segment
consisting of a closed-cell segment; each closed-cell segment
consisting solely of at least one annular closed-cell ring formed
by struts defining a plurality of closed-cell elements having a
plurality of proximal and distal peaks and valleys; each Z-segment
consisting solely of at least one annular Z-ring formed by struts
defining an elongate member including a plurality of wave-shape
portions having a plurality of proximal and distal peaks and
valleys; and wherein the other of said pair of stent modules
comprising a first Type B module including, an intermediate segment
consisting of a said closed-cell segment; and a pair of end
segments connected to respective longitudinal ends of said
intermediate segment, each end segment consisting of a said
Z-segment; and wherein an end segment of said first Type A module
is connected to an end segment of said first Type B module.
2. A modular stent as recited in claim 1 wherein each closed-cell
ring is formed by a pair of opposed Z-rings tightly interconnected
at pairs of facing peaks or pairs of facing valleys or pairs of
facing peaks and valleys.
3. A modular stent as recited in claim 4 wherein each closed-cell
ring is formed by a pair of opposed, interconnected longitudinally
aligned Z-rings defining a plurality of pairs of facing aligned
peaks and a plurality of pairs of facing aligned valleys.
4. A modular stent as recited in claim 5 wherein in each of said
closed-cell rings, linear interconnectors interconnect every pair
of facing aligned peaks to define hexagonal-shaped closed-cell
elements.
5. A modular stent as recited in claim 5 wherein in each of said
closed-cell rings, the facing aligned peaks of every pair of facing
aligned peaks are directly connected to each other.
6. A modular stent as recited in claim 1 wherein each of said
closed-cell elements are formed by linear struts.
7. A modular stent as recited in claim 1 wherein each of said
Z-rings comprise substantially linear struts.
8. A modular stent as recited in claim 1 wherein each pair of
longitudinally adjacent annular rings are interconnected to each
other by interconnectors.
9. A modular stent as recited in claim 8 wherein said
interconnectors comprise linear interconnectors.
10. A modular stent as recited in claim 8 wherein said
interconnectors have a thickness greater than the thickness of said
struts forming said closed-cell elements.
11. A modular stent as recited in claim 1 wherein each closed-cell
segment includes at least one closed-cell ring having from 4 to 16
closed-cell elements defining from 4 to 16 proximal and distal
peaks and valleys.
12. A modular stent as recited in claim 1 wherein each Z-segment
includes at least one Z-ring defining from 4 to 16 distal and
proximal peaks and valleys.
13. A modular stent as recited in claim 1 wherein each closed-cell
segment includes from 1 to 4 closed-cell annular rings.
14. A modular stent as recited in claim 1 wherein each Z-segment
includes from 1 to 8 Z-rings.
15. A modular stent as recited in claim 1 wherein each closed-cell
segment includes from 1 to 4 closed-cell rings, each closed-cell
ring having from 4 to 16 closed-cell elements and from 4 to 16
distal and proximal peaks; and each Z-segment includes from 1 to 8
Z-rings, each Z-ring having from 4 to 16 distal and proximal
peaks.
16. A modular stent as recited in claim 15 wherein longitudinally
adjacent distal and proximal annular rings are interconnected by
interconnectors.
17. A modular stent as recited in claim 16 wherein said
interconnectors interconnect distal peaks or valleys of a proximal
annular ring to proximal peaks or valleys of a distal annular
ring.
18. A modular stent as recited in claim 17 wherein an
interconnector interconnects every third one of said distal peaks
or valleys of said proximal annular ring to every third one of said
proximal peaks or valleys of said distal annular ring.
19. A modular stent as recited in claim 17 wherein an
interconnector has either a linear or a non-linear shape and a
thickness of up to twice the thickness of struts forming said
annular rings.
20. A modular stent as recited in claim 1 constituted by at least
three of said modules, including: an intermediate module comprising
said first Type B module consisting solely of an intermediate
closed-cell segment and proximal and distal end Z-segments; and a
pair of proximal and distal Type A modules interconnected to
respective ends of said intermediate Type B module, said proximal
Type A module comprising said first Type A module and said distal
Type A module comprising a second Type A module, each Type A module
consisting solely of an intermediate Z-segment and proximal and
distal end closed-cell segments.
21. A modular stent as recited in claim 20 wherein said
intermediate closed-cell segment of said intermediate Type B module
consists solely of a single closed-cell ring.
22. A modular stent as recited in claim 21 wherein each of said end
segments of said intermediate Type B module consists solely of four
Z-rings.
23. A modular stent as recited in claim 20 wherein said
intermediate Z-segment of each of said pair of Type A modules
includes four Z-rings.
24. A modular stent as recited in claim 23 wherein said end
closed-cell segments of each of said pair of Type A modules include
a single closed-cell ring.
25. A modular stent as recited in claim 49 wherein: said
intermediate Type B module consists solely of an intermediate
closed-cell segment consisting solely of a single closed-cell ring,
and a pair of end Z-segments consisting solely of four Z-rings; and
wherein each of said proximal and distal Type A modules consists
solely of an intermediate Z-segment consisting solely of four
Z-rings, and a pair of end closed-cell segments, each consisting
solely of a single closed-cell ring.
26. A modular stent as recited in claim 25 wherein each of
longitudinally adjacent rings are aligned and interconnected to
each other by interconnectors situated at least at every third pair
of facing aligned peaks.
27. A modular stent as recited in claim 1 wherein said stent is
formed of fenestrated wire.
28. A modular stent as in claim 1 wherein said stent is formed of a
shape-memory alloy.
29. A modular stent as in claim 28 wherein said shape-memory alloy
comprises superelastic nitinol.
30. A modular stent as in claim 28 wherein said stent is formed of
tubular material.
31. A modular stent as in claim 30 wherein said tubular material
comprises a small diameter tube corresponding to the diameter of a
fully collapsed stent, which is laser cut and expanded to said
expanded tubular configuration.
32. A modular stent as recited in claim 28 wherein said stent is
formed of a wire material.
33. A modular stent as in claim 1 wherein said stent comprises a
balloon expandable stent.
34. A modular stent as in claim 20 wherein each closed-cell segment
includes from 1 to 4 closed-cell rings, each closed-cell ring
having from 4 to 16 closed-cell elements; and wherein each
Z-segment includes from 1 to 8 Z-rings, each Z-ring having from 4
to 16 proximal and distal peaks.
35. A modular stent as in claim 20 wherein each closed-cell segment
includes from 1 to 4 closed-cell element annular rings, each
closed-cell annular ring having from 4 to 16 closed-cell elements;
and wherein each Z-segment includes from 1 to 8 Z-rings, each
Z-ring having from 4 to 16 proximal and distal peaks.
36. A modular stent as recited in claim 1 having an outermost
annular ring at each longitudinal end of the stent and wherein a
radiopaque marker is applied to at least one of said outermost
annular rings of the stent.
37. A modular stent as in claim 36 wherein radiopaque markers are
applied to both of said outermost annular rings of the stent.
38. A modular stent as in claim 36 wherein a radiopaque marker is
applied to outermost peaks of said at least one of said outermost
annular rings of the stent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S. patent
application Ser. No. 10/333,600, filed Jan. 21, 2003, which in turn
is a National Phase filing of PCT patent application No.
PCT/US2002/38456, filed Dec. 3, 2002 and designating the United
States, and expired U.S. provisional patent application Ser. No.
60/337,060, filed Dec. 3, 2001, all of which are incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates generally to medical devices, and
more particularly to radially expandable stents for holding vessels
such as arteries for open flow, and to methods for manufacturing
stents.
BACKGROUND OF THE INVENTION
[0003] A stent is a generally longitudinal cylindrical device
formed of biocompatible material, such as metal or plastic, which
is used in the treatment of stenosis, strictures, or aneurysms in
body blood vessels and other tubular body structures, such as the
esophagus, bile ducts, urinary tract, intestines or the
tracheo-bronchial tree.
[0004] A stent is held in a reduced diameter unexpanded
configuration within a low profile catheter until delivered to the
desired location in the tubular structure, most commonly a blood
vessel, whereupon the stent radially expands to an expanded
diameter configuration in the larger diameter vessel to hold the
vessel open. Radial expansion may be accomplished by an inflatable
balloon attached to a catheter, or the stent may be of the
self-expanding type that will radially expand once released from
the end portion of the delivery catheter. A fundamental concern is
that the stent be as completely apposed to the vessel wall as
possible, exerting maximal focal radial forces at the site of the
narrowing.
[0005] Generally, there are several desired objectives in designing
a stent. One objective is to provide the stent with an optimal
distribution of radial forces along its length in its expanded
configuration so that the stent provides a uniform, high radial
force in the stenosed region of the vessel but a lower radial force
in healthy parts of the vessel where high forces are not necessary.
A stent should be able to counteract two main extrinsic forces,
namely the elastic recoil of the atherosclerotic plaque and the
adjacent non-diseased vessel wall, and active contraction of smooth
muscle fiber within the vessel wall. In addition, the stent should
be maximally apposed to the vessel wall to minimize the relative
motion between the vessel wall and the struts from which the stent
is constructed, which may result in intimal trauma. The stent
should exert enough focal radial force to open the narrowed
segment. However, the remaining vessel segments do not necessarily
need to be exposed to these stretching forces.
[0006] Another objective in stent design is to provide the stent
with a high degree of flexibility in its unexpanded or collapsed
configuration in order to facilitate maneuvering within tortuous
vessels during delivery, as well as optimum flexibility of the
stent in its expanded configuration for better wall apposition when
deployed within tortuous vessels. It has been demonstrated
experimentally that better apposition of the stent struts to the
vessel wall is associated with improved long-term patency of the
stented vessel. A stent which is not completely apposed to the
vessel wall results in more exuberant intimal response and a higher
incidence of restenosis. Poor stent apposition in a pulsating
artery may be associated with repetitive micro trauma to the vessel
wall, again resulting in an increase in the incidence of clot
formation and restenosis.
[0007] The apposition to the vessel wall should be balanced with
the "metal to wall" ratio, meaning that the healthy vessel should
be exposed to the least surface area of the metallic stent.
[0008] At the same time the diseased segment should be exposed to
the minimum force required to open it wide, while preventing the
plaque from extending and protruding through the stent struts.
[0009] Another criteria of stent design is to provide a flexible
stent which is also kink resistant in order to decrease overlapping
of stent struts and the protrusion of exposed edges of the struts
of a curved stent into the wall of a tortuous vessel.
[0010] Stents in actual use today are generally uniform in their
design and for the most part are constructed from interconnected
struts forming either a plurality of identical interconnected
annular Z-rings or a plurality of identical interconnected annular
closed-cell rings. Each type of ring possesses the main inherent
feature of radial expansion following deployment. The closed-cell
rings can incorporate different cell designs, which are intended to
provide better radial forces and wall apposition.
[0011] Multi-segment stents, i.e. stents having a non-uniform
design including both Z-rings and closed-cell rings, have been
described in the prior art and are designed as such for different
purposes. Examples of such stent designs are shown in U.S. Pat. No.
5,064,435 to Porter; U.S. Pat. No. 5,354,308 to Simon; U.S. Pat.
No. 5,569,295 to Lam; U.S. Pat. No. 5,716,393 to Lindenberg; U.S.
Pat. No. 5,746,765 to Kleshinski; U.S. Pat. No. 5,807,404 to
Richter et al; U.S. Pat. No. 5,836,966 to St. Gennthn; U.S. Pat.
No. 5,938,697 to Killion; U.S. Pat. No. 6,146,403 to St. Germain;
U.S. Pat. No. 6,159,238 to Killion; U.S. Pat. No. 6,187,034 to
Frantzen; U.S. Pat. No. 6,231,598 to Berry et al.; U.S. Pat. No.
6,106,548 to Roubin et al.; U.S. Pat. No. 6,066,168 to Lau et al.;
U.S. Pat. No. 6,325,825 to Kula et al.; U.S. Pat. No. 6,348,065 to
Brown et al.; U.S. Pat. No. 6,355,057 to DeMarais et al and U.S.
Pat. No. 6,355,059 to Richter et al. Some of these designs attempt
to address problems which are encountered in clinical practice
including inadequate wall apposition, overlapping of neighboring
struts and incomplete cell expansion leading to insufficient radial
force distribution. Some of them are constructed to provide
variable radial forces while some are designed to be flexible to
maintain good wall apposition. However, the stents described in the
prior art generally are specifically designed to provide only one
or two of these features and therefore only meet a limited number
of the desired objectives.
[0012] Stents are typically manufactured from thin tubes which are
slotted by a laser beam to define a series of closely-packed
struts. However, this technique has certain problems and
limitations. One problem is in the manufacture of self expanding
stents which are not uniform in design, e.g. multi-segment stents.
Such stents are typically manufactured from thin tubes of shape
memory alloy which are slotted by a laser beam to define a
plurality of interconnected closed-cell rings and Z-rings, and then
mechanically expanding the tubes on mandrels to progressively
greater diameters and at the same time heat treating them to impart
the desired temperature-shape memory characteristics. However, as a
non-uniform multi-segment stent is mechanically expanded, the
struts forming the annular rings are subjected to asymmetrical
forces resulting in irregular or distorted closed-cell and Z-ring
geometry. This irregular geometry is "memorized" by the stent so
that upon delivery to and expansion in a stenosed region of a
vessel, it will not provide optimal force distribution or wall
apposition.
[0013] Another problem arises in the manufacture of stents from a
laser slotted tube when it is desired that the tube wall be very
thin so that the struts formed from the slotted tube wall are
correspondingly thin, such as when the stent is to be expanded in a
small diameter vessel. In order to prevent the thin tube material
at the vertices of intersecting struts from tearing as the tube is
expanded during manufacture, it has been necessary for the slots
formed by the laser beam to be a certain, relatively large, width
to provide a large radius curvature at the vertices of the struts
to relieve the stresses in those regions as the tube expands.
However, this limits the width of the struts.
[0014] Still another problem in the manufacture of non-uniform
multi-segment stents comprising a plurality of interconnected
closed-cell rings and Z-rings by laser-cutting and then expanding
small diameter tubes is that it is often costly and time consuming
to create specific software for guiding the laser cutting tool to
cut the particular desired sequence and configuration of
closed-cell rings and Z-rings. The need to create specific laser
cutting tool software for a particular predetermined desired
sequence and arrangement of closed-cell rings and Z-rings for a
stent has impeded the widespread adoption and use of multi-segment
stents having annular rings sequenced and arranged to provide
optimal characteristics for a particular clinical application.
SUMMARY OF THE INVENTION
[0015] It is therefore an object of the present invention to
provide a new and improved stent designed to provide optimal
features for a wide range of clinical applications.
[0016] Another object of the present invention is to provide a new
and improved stent designed to provide optimal radial forces,
flexibility and kink resistance for a wide range of clinical
applications.
[0017] Still another object of the present invention is to provide
a new and improved stent designed to provide optimal radial forces,
flexibility and kink resistance taking into account specific
anatomic locations of the lesion or stenosis and the geometry and
other characteristics of the lesion or stenosis.
[0018] A further object of the present invention is to provide a
new and improved stent designed to optimally distribute radial
forces along its length.
[0019] A still further object of the present invention is to
provide a new and improved stent with a high degree of flexibility
in its unexpanded configuration for maneuvering within tortuous
vessels during delivery.
[0020] Yet another object of the present invention is to provide a
new and improved stent with optimal flexibility in its expanded and
deployed condition for improved wall apposition in tortuous
vessels.
[0021] A still further object of the present invention is to
provide a new and improved flexible stent which is kink resistant
to decrease the exposure of sharp edges of the struts of the stents
in tortuous vessels.
[0022] Another object of the present invention is to provide new
and improved methods for manufacturing stents.
[0023] A further object of the present invention is to provide new
and improved methods for manufacturing multi-segment stents.
[0024] A still further object of the present invention is to
provide new and improved methods for manufacturing stents having
very thin struts.
[0025] Briefly, these and other objects are attained by providing a
stent having a modular construction constituted by a single module
or a plurality of interconnected modules, each module including an
intermediate segment consisting of one of either a closed-cell
segment or a Z segment, and a pair of end segments connected by
interconnector elements to respective axial ends of said
intermediate segment, each end segment consisting of the other of
said closed-cell segment or Z-segment. Each Z-segment consists
solely of at least one annular Z-ring formed by an elongate member
shaped or constructed to include a plurality of generally
sinusoidal or wave-shape portions defining proximal and distal
peaks and valleys. Each closed-cell segment consists solely of at
least one annular ring formed by a pair of longitudinally adjacent
Z-rings which are tightly interconnected to each other to form a
ring of circumferentially interconnected closed-cell elements
defining proximal and distal peaks and valleys. In an embodiment in
which the module is designated a "Type A" module, the intermediate
segment comprises a Z-segment and each of the pair of end segments
comprises a closed-cell segment. In another embodiment in which the
module is designated a "Type B" module, the intermediate segment
comprises a closed-cell segment and each of the pair of end
segments comprises a Z-segment.
[0026] Preferably, the stents are formed of modules in which each
closed-cell segment of a module comprises from one to four
closed-cell rings and each Z-segment of a module comprises from one
to eight Z-rings.
[0027] Each Z-ring and each closed-cell ring preferably defines
from four to sixteen distal and proximal peaks and valleys.
Longitudinally adjacent pairs of rings are interconnected by
interconnector elements connected to opposed or offset pairs of
peaks and/or valleys of the connected rings, and in the case of
adjacent closed-cell rings, by shared walls or struts of the
closed-cells.
[0028] Stents formed of one or more modules having the aforesaid
construction will possess three desirable characteristics namely, a
distribution of radial force along the length of the stent
appropriate for any particular case, a high degree of kink
resistance and a high degree of longitudinal flexibility (in both
unexpanded and expanded configurations) thereby making such a stent
suitable for a wide range of applications.
[0029] For example, a stent in accordance with the invention can
provide strong radial forces along a stenosed portion of a vessel
which shows the largest burden of atherosclerotic plaque by
covering this area with closed-cell segments, which have higher
radial force and stability. Depending on the length of these
lesions closed-cell segments can be constructed of one or more
rings to cover the entire area of the stenosis.
[0030] A multi-segment modular stent having this construction is
also particularly suited for use in portions of vessels having
sharp turns. In such cases, a closed-cell segment is preferably
situated at the apex of a sharp turn in the vessel to prevent
kinking of the stent and maintain good patency and flow through the
stent. This construction also eliminates exposure of free edges of
stent struts at the bend. An area of significant narrowing at the
apex of a curvature of a vessel should be covered with a closed
cell segment of the modular stent to prevent kinking, as well as
for providing greater radial support. The adjacent Z-segments will
allow the device to conform to the angles and tortuous geometry of
the vessel.
[0031] Tortuous portions of a vessel without any significant
narrowing are covered with Z-ring segments. In the case of an
S-shaped vessel configuration with a mild disease along its entire
length, it is beneficial to place a long segment of Z-rings to
cover this area. Z-segments should also be positioned at the turns
of a vessel between significant tandem lesions, which should be
covered with closed-cell segments.
[0032] In cases of relatively straight vessels it is beneficial to
use modular stents with closed-cell segments at both ends for
better anchoring and stability. On the other hand if portions of a
vessel immediately adjacent to an area of significant narrowing are
tortuous or have bends, it would be better to use a modular stent
with Z-ring segments at the ends for better apposition to the
vessel wall.
[0033] The multi-segment modular construction also provides
stability to the stent to minimize frictional motion resulting from
vessel pulsation. This motion is believed to contribute to constant
microtrauma and aseptic inflammatory changes within the vessel
wall, which in turn results in formation of excessive neointima
which grows through the stent struts causing eventually
restenosis.
[0034] A long modular stent constructed according to the invention
can be used in patients who otherwise require placement of more
than one standard stent. This technique will avoid both the
undesirable overlap of stents, which often leads to higher
incidence of more prominent intimal hyperplasia and restenosis, and
the potential for leaving uncovered gaps between stents, which can
lead to protrusion of an atherosclerotic plaque and flow
compromise. Long modular stents can be built to accommodate complex
vessel shapes which are difficult or impossible to cover with
sequential placement of several standard stents.
[0035] A stent of the present invention may be constructed from a
shape memory alloy such as nitinol for self-expanding stents or
from stainless steel or other alloys for balloon-expandable stents.
The self-expanding stent expands spontaneously as a result of
superelasticity combined with the shape memory effect of exposure
to body temperature and in several designs presented herein, is
designed to exhibit minimal or no foreshortening.
[0036] In order to manufacture multi-segment self-expanding stents
having a particular predetermined desired sequence and arrangement
of closed-cell rings and Z-rings, with the rings all having a
regular, undistorted geometry, in accordance with the invention,
the small diameter tube is laser-cut to define a plurality of
longitudinally adjacent Z-rings interconnected by interconnector
portions so that every pair of adjacent Z-rings constitutes a
closed-cell ring. The tube is expanded and heat-treated, and then
certain ones of the interconnector portions are removed from the
expanded tube to provide the predetermined desired sequence and
arrangement of interconnected closed-cell rings and Z-rings. All of
the interconnector portions, including the interconnector portions
which are eventually removed, serve to maintain the regular
geometry of the rings during expansion and heat treatment of the
tube.
[0037] In order to manufacture stents from a very thin-walled
laser-slotted tube with wide struts without risking tearing the
tube material at the vertices of intersecting struts, in accordance
with the invention, the slots cut in the small diameter tube that
define the struts are themselves made very thin with enlarged
diameter openings formed at the ends of the slots defining the
vertices between adjacent struts to relieve the stress raised in
the regions of the vertices during expansion of the tube. By
narrowing the slots, the width of the struts can be increased.
[0038] Finally, in order to facilitate the manufacture and use of
multi-segment stents, stent blanks are initially prepared, which
may be done even before the desired sequence and arrangement of the
Z-rings and closed-cell rings have been determined. A blank is
formed by laser-cutting a small diameter tube of shape-memory
material to define a plurality of pairs of longitudinally adjacent
Z-rings having interconnector portions integrally joining the
Z-rings of each pair in a manner such that every pair of adjacent
Z-rings constitutes a closed-cell ring. The small diameter tube is
then expanded and heat treated to form a stent blank. Once the
particular intended application of the stent is known, the
particular desired sequence and arrangement of the interconnected
closed-cell rings and Z-rings are determined. Certain ones of the
interconnector portions are then removed from the blank, either
mechanically or using a laser tool, in order to provide the desired
arrangement and sequence of the closed-cell rings and Z-rings. This
technique enables an inventory of blanks for multi-segment stents
to be maintained so that once a particular clinical application is
determined for a stent, it is a simple and quick matter to obtain
an appropriate stent blank and remove appropriate interconnector
portions to provide the stent with optimal features for the
particular application.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] A more complete appreciation of the present invention and
many of the attendant advantages thereof will be readily understood
by reference to the following detailed description when considered
in connection with the accompanying drawings in which:
[0040] FIG. 1(a) shows one embodiment of a Z-ring in its expanded
configuration, cut longitudinally and flattened into a plane;
[0041] FIG. 1(b) is similar to FIG. 1(a) and shows another
embodiment of a Z-ring;
[0042] FIGS. 2(a)-2(1) show different embodiments of closed-cell
rings in expanded configurations, cut longitudinally and flattened
into a plane;
[0043] FIG. 3 shows the angle between two struts forming a peak of
a Z-ring, or a peak of a closed-cell ring, in an expanded
configuration;
[0044] FIG. 4 shows the distance d between the distal and proximate
peaks of two longitudinally adjacent annular rings in an expanded
configuration;
[0045] FIGS. 5(a)-5(g) show pairs of longitudinally adjacent
Z-rings interconnected by different embodiments of interconnectors
in expanded configurations, cut longitudinally and flattened;
[0046] FIG. 6 shows a hexagonal type closed-cell ring formed of a
pair of longitudinally adjacent Z-rings interconnected to each
other by interconnectors at every pair of opposed peaks, in an
expanded configuration, cut longitudinally and flattened;
[0047] FIG. 7 shows a pair of longitudinally adjacent closed-cell
rings interconnected by linear interconnector elements, in an
expanded configuration, cut longitudinally and flattened;
[0048] FIGS. 8(a)-8(c) show pairs of longitudinally adjacent
closed-cell rings interconnected by interconnector elements in the
form of shared walls, in expanded configurations, cut
longitudinally and flattened;
[0049] FIG. 9 shows an embodiment of a Type A stent module in
accordance with the present invention in an expanded configuration,
cut longitudinally and flattened;
[0050] FIG. 10 shows an embodiment of a Type B stent module in
accordance with the present invention in an expanded configuration,
cut longitudinally and flattened;
[0051] FIG. 11 shows another embodiment of a Type A stent module in
accordance with the present invention, in an expanded
configuration, cut longitudinally and flattened;
[0052] FIG. 12 shows another embodiment of a Type B stent module in
accordance with the present invention in an expanded configuration,
cut longitudinally and flattened;
[0053] FIG. 13 shows two Type A stent modules interconnected by
shared walls of closed-cell elements of adjacent annular
closed-cell rings, in an expanded configuration, cut longitudinally
and flattened;
[0054] FIG. 14 shows the two Type A stent modules of FIG. 13, but
interconnected by linear interconnectors connecting opposed peaks
of adjacent closed-cell rings, in an expanded configuration, cut
longitudinally and flattened;
[0055] FIG. 15 shows an embodiment of a stent in accordance with
the present invention formed of an intermediate Type B module and a
pair of Type A modules interconnected to the ends of the Type B
module, in an expanded configuration, cut longitudinally and
flattened;
[0056] FIG. 16 is a front elevation view of another embodiment of a
stent in accordance with the present invention formed of an
intermediate Type B module and a pair of Type A modules
interconnected to the ends of the Type B module;
[0057] FIG. 17 is a front elevation view of the stent shown in FIG.
16, shown in its expanded configuration and bent about 1800;
[0058] FIG. 18 is a front elevation view of the stent shown in
FIGS. 16-17, shown in its expanded configuration and situated
within an S-shaped tortuous vessel;
[0059] FIG. 19 shows a laser-slotted tube constituting the stent
shown in FIGS. 16-18 in an unexpanded configuration, cut
longitudinally and flattened;
[0060] FIG. 20 shows another embodiment of a Type A stent module in
accordance with the present invention adapted for placement across
a side branched vessel, in an expanded configuration, cut
longitudinally and flattened;
[0061] FIG. 21 is a schematic perspective view showing a hollow
fenestrated wire for forming a stent according to the present
invention through which fluids, such as medication, can be
delivered;
[0062] FIG. 22 shows another embodiment of a stent in accordance
with the present invention formed of an intermediate Type B module
and a pair of Type B modules interconnected to the ends of the
intermediate Type B module, in an expanded configuration, cut
longitudinally and flattened;
[0063] FIG. 23 shows another embodiment of a stent in accordance
with the present invention formed of an intermediate Type B module
and a pair of Type A modules interconnected to the ends of the
intermediate Type B module, in an expanded configuration, cut
longitudinally and flattened;
[0064] FIG. 24(a) shows a portion of a laser-slotted tube, cut
longitudinally and flattened;
[0065] FIG. 24(b) shows a step of a progressive mechanical
expansion of the laser-slotted tube shown in FIG. 24(a), cut
longitudinally and flattened;
[0066] FIG. 25(a) shows a portion of a laser-slotted tube used in
stent manufacture, according to the present invention, cut
longitudinally and flattened;
[0067] FIG. 25(b) shows a magnified area, designated B, of the
laser-slotted tube shown in FIG. 25(a);
[0068] FIG. 25(c) shows a step of a progressive mechanical
expansion of the laser-slotted tube shown in FIGS. 25(a) and 25(b)
during manufacture according to the present invention;
[0069] FIG. 25(d) shows a stent manufactured from the expanded
laser-slotted tube shown in FIGS. 25(a)-25(c), cut longitudinally
and flattened;
[0070] FIG. 25(e) is a view similar to FIG. 25(b) showing another
embodiment of a laser-slotted tube used in stent manufacture,
according to the present invention;
[0071] FIG. 26(a) shows a portion of a thin-walled laser-slotted
tube;
[0072] FIG. 26(b) is a view similar to FIG. 26(a) showing a portion
of a thin-walled laser-slotted tube, slotted according to another
aspect of the manufacturing methods of the invention;
[0073] FIG. 27 is a front elevation view of a tapered stent in
accordance with the present invention formed of an intermediate
Type B module and a pair of Type A modules interconnected to the
ends of the intermediate Type B module;
[0074] FIG. 28(a) shows a first embodiment of a stent blank in
accordance with the invention, cut longitudinally and
flattened;
[0075] FIGS. 28(b) and 28(c) show different stents manufactured
from the stent blank of FIG. 28(a), cut longitudinally and
flattened;
[0076] FIG. 29(a) shows a second embodiment of a stent blank in
accordance with the invention, cut longitudinally and
flattened;
[0077] FIGS. 29(b), 29(c) and 29(d) show different stents
manufactured from the stent blank of FIG. 28(a), cut longitudinally
and flattened;
[0078] FIG. 30(a) shows a third embodiment of a stent blank in
accordance with the invention, cut longitudinally and flattened;
and
[0079] FIGS. 30(b) and 30(c) show different stents manufactured
from the stent blank of FIG. 30(a), cut longitudinally and
flattened.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0080] A stent in accordance with the invention has a modular
construction constituted by a combination of interconnected
segments of annular Z-rings and closed-cell rings. Each module is
formed of three segments including an intermediate segment
comprising either a closed-cell segment or a Z-segment and a pair
of end segments comprising the other of closed-cell or
Z-segments.
[0081] Referring now to the drawings wherein like reference
characters designate identical or corresponding parts throughout
the several views, and more particularity to FIG. 1(a), a Z-ring
100a comprises struts 1 which together define a plurality of "Z" or
sinusoidal or wave shapes. The struts 1 may be formed by expanding
a laser-slotted metallic tube, or from portions of a single wire,
or from individual wire elements, or by any other method of
construction known to those skilled in the art. The mesh design of
the stent can be laser cut from a large diameter tube, which is
equal to the final diameter of a fully expanded stent or which may
be further expanded to an even larger diameter. This technological
process enables the steps of expansion and heat treatment steps to
be avoided and enables perfectly uniform shape of the cells
throughout the stent to be achieved. However larger tubes are more
expensive and there is substantial amount of wasted material.
during the laser cutting process.
[0082] The Z-ring 100a has twelve distal peaks P(z)d and twelve
proximal peaks P(z)p constituted by the most distal and most
proximal longitudinal edge surfaces of the ring 100a. The distal
longitudinal direction is designated in this and other drawing
figures by arrow L, i.e. upward toward the top of the page. In this
case, the peaks P(z)d, P(z)p are the outermost edge surfaces of the
vertices of pairs of intersecting struts 1. Twelve distal and
proximal valleys V(z)d and V(z)p are constituted by the innermost
edge surfaces associated with each peak on the distal and proximal
sides of the Z-ring, i.e. facing in the distal and proximal
directions. In this case the valleys V(z)d, V(z)p are at the inner
sides of the vertices of pairs of intersecting struts 1.
[0083] While the struts of the Z-ring 100a shown in FIG. 1(a) are
integrally formed with each other and intersect each other at sharp
points, the Z-rings can have other forms. For example, referring to
FIG. 1(b), an annular Z-ring 100b comprises twelve integral smooth
sinusoidal waves having peaks P(z)d, P(z)p and valleys V(z)d,
V(z)p. Z-rings forming Z-segments of a stent module in accordance
with the invention preferably comprise between four and sixteen
distal and proximal peaks P(z)d and P(z)p and valleys V(z)d and
V(z)p over their circumference.
[0084] Referring to FIG. 2, closed-cell rings are shown formed by
pairs of tightly interconnected longitudinally adjacent Z-rings.
The Z-rings can either be longitudinally aligned, i.e. mutually
positioned with their pairs of proximate peaks (and their proximate
valleys) P(z)p and P(z)d in longitudinal alignment, indicated by
the longitudinally extending line A in FIG. 2(a) which passes
through proximate aligned peaks, or longitudinally offset, i.e.
mutually positioned with their proximate peaks P(z)p and P(z)d
being offset from each other, indicated by the oblique line A1 in
FIG. 2(i), which passes through proximate offset peaks P(z)p and
P(z)d. In this case (e.g. FIG. 2(i)), each peak in one Z-ring is
longitudinally aligned with a respective proximate valley in the
other Z-ring as indicated by the line A2 in FIG. 2(i). By "tightly
interconnected" is meant that the Z-rings are connected to each
other at every, or at every other, pair of proximate aligned or
proximate offset peaks or valleys or their combination.
[0085] As seen in FIG. 2(a), a closed-cell ring 200a having a
plurality of interconnected hexagonal-shaped closed-cell elements
C, is formed by interconnecting two aligned Z-rings 100d and 100p
at every pair of facing proximal and distal peaks P(z)p, P(z)d of
distal and proximal Z rings 100d and 100p, by means of straight,
longitudinally extending interconnectors T. A closed cell ring of
this type has a high radial strength, a high degree of kink
resistance, low flexibility and a relatively high degree of
foreshortening upon expansion from its collapsed state.
[0086] Referring to FIG. 2(b), a closed-cell ring 200b having a
plurality of interconnected closed-cell elements C is formed by
interconnecting two aligned Z-rings 100d and 100p at every other
pair of facing peaks P(z)p and P(z)d with linear and longitudinal
interconnectors T. This type of closed-cell ring will provide less
radial strength, less kink resistance, somewhat more flexibility
and the same degree of foreshortening as the closed-cell ring 200a
shown in FIG. 2(a). Closed-cell rings of this type have large open
areas and therefore provide a smaller metal to vessel wall ratio,
which may be beneficial in certain clinical situations, but at the
same time can allow prolapse of atherosclerotic material through
the interstices.
[0087] A closed-cell annular ring 200c, shown in FIG. 2(c), having
a plurality of closed-cell elements C, is formed by interconnecting
every proximal valley V(z)p of a distal Z-ring 100d with every
facing distal valley V(z)d of an aligned proximal Z-ring 100p by a
linear longitudinal interconnector T. This type of closed-cell ring
is comparable in flexibility and kink resistance to the one shown
in FIG. 2(a). It has somewhat less radial strength, but has a
benefit of less foreshortening upon expansion as compared to the
design shown in FIG. 2(a). Referring to FIG. 2(d), a closed-cell
ring 200d having a plurality of closed-cell elements C is shown
which is similar to ring 200c of FIG. 2(c), with the exception that
every other pair of opposed valleys V(z)p and V(z)d are
interconnected, thereby increasing the area enclosed by each
individual closed-cell, and reducing the overall metal to vessel
wall ratio. It has slightly less radial force and kink resistance,
slightly more flexibility and the same degree of foreshortening as
the design shown on FIG. 2(c). Referring to FIG. 2(e), a
closed-cell annular ring 200e having a plurality of closed-cell
elements C is formed by interconnecting every proximal valley V(z)p
of a distal Z-ring 100d with the facing distal peak P(z)d of an
offset proximal Z-ring 100p by linear longitudinal interconnectors
T. The annular ring 200e has less radial strength, similar
flexibility and kink resistance, but a slightly less degree of
foreshortening as compared to the design shown in FIG. 2(a). It has
more prominent foreshortening compared to the design shown in FIG.
2(c). Referring to FIG. 2(f), closed-cell ring 200f is shown formed
of a plurality of closed-cell elements C having a construction
similar to that shown in FIG. 2(e), except that every other pair of
facing proximal valleys V(z)p and distal peaks P(z)d of offset
distal and proximal Z-rings 100d and 100p are interconnected,
resulting in larger open areas for the individual closed cell
elements C and a smaller overall metal to vessel wall ratio.
Referring to FIG. 2(g), a closed-cell ring 200g is formed including
a plurality of closed-cell elements C by interconnecting every
other distal valley of the V(z)d of proximal Z-ring 100, with every
other aligned proximal peak of the offset distal Z-ring 100d by
linear longitudinal interconnectors T. This closed-cell ring 200g
has identical features to the closed-cell ring 200(f) shown in FIG.
2(f). Referring to FIG. 2(h), a closed-cell ring 200h formed of
closed-cell elements C is formed by interconnecting every pair of
aligned proximal peaks P(z)p and distal valleys V(z)d of offset
distal and proximal Z-rings 100d and 100p with linear longitudinal
interconnectors T. The closed-cell ring 200h has identical features
to the ring 200e shown in FIG. 2(e). Referring to FIG. 2(i), a
closed-cell annular ring 200i is formed by a pair of offset Z-rings
100d and 100, by interconnecting every distal peak P(z)d of
proximal Z-ring 100, with every facing proximal peak P(z)p of
offset Z-ring 100d with a linear, obliquely extending
interconnector T. Closed-cell ring 200i includes a plurality of
quadrilateral closed-cell elements C and has a higher degree of
stability than the closed-cell rings described above. Referring to
FIG. 20), a closed-cell annular ring 200j including closed-cell
elements C is formed by a pair of offset proximal and distal
Z-rings 10; and 100d by interconnecting every other distal peak
P(z)d of proximal Z-ring 100p with a facing proximal peak P(z)p of
distal Z-ring 100d. A closed-cell ring 200j provides a higher
degree of flexibility and less radial strength compared to the
closed-cell ring 200i of FIG. 2(i). As shown in FIG. 2(k), a
closed-cell ring 200k is formed by directly, i.e without linear
interconnectors, connecting every pair of opposed peaks P(z)p, and
P(z)d of aligned distal and proximal Z-rings 100d and 100p. As
shown in FIG. 2(1), a closed-cell ring 200l can also be formed by
directly connecting every other pair of opposed peaks P(z)p, and
P(z)d of adjacent aligned Z-rings 100d and 100p.
[0088] Each of the closed-cell rings 200 shown in FIG. 2 has its
own proximal and distal peaks P(c)p and P(c)d and proximal and
distal valleys V(c)p and V(c)d. The proximal peaks P(c)p and
proximal valleys V(c)p of each closed-cell ring 200 correspond to
the proximal peaks P(z)p and proximal valleys V(z)p of the proximal
Z-ring 100p forming part of the closed-cell ring 200 while the
distal peaks P(c)d and distal valleys V(c)d of each closed-cell
ring 200 correspond to the distal peaks P(z)d and distal valleys
V(z)d of the distal Z-ring 100d forming part the closed-cell ring
200.
[0089] Closed-cell rings forming closed-cell segments of a stent
module in accordance with the invention preferably comprise between
four and sixteen distal and proximal peaks P(c)d and P(c) and
valleys V(c)d and V(c)p over their circumference.
[0090] Stents in accordance with the present invention are
constructed of both closed-cell rings and Z-rings in a particular
modular arrangement to achieve an optimal combination of several
main characteristics, including appropriate radial force
distribution in the axial direction, good longitudinal flexibility,
in both expanded and unexpanded configurations, good kink
resistance, and reduced foreshortening upon expansion. Longitudinal
stent portions that comprise closed-cell segments generally exhibit
greater radial force, and lesser flexibility, i.e. greater
stiffness, than stent portions formed of Z-segments. Struts forming
closed-cell rings and closed-cell segments have greater geometric
stability than struts forming Z-rings and Z-segments. For this
reason, stent portions comprising closed-cell segments exhibit less
relative motion between the stent struts and the vessel wall than
do stent portions formed of Z-segments. Increased stability of the
stent struts with consequent decrease in relative movement between
the stent and the apposed vessel wall results in a reduced
potential for inflammation of the vessel wall.
[0091] Compared to stent portions formed of Z-segments, stent
portions formed of closed-cell segments exhibit increased kink
resistance and therefore improved integrity of the inner lumen of
the stent. Stents portions formed of Z-segments generally tend to
kink to a greater extent even in vessels having relatively small
bends. Kinking of stent portions formed of Z-segments results in
overlapping of, and interference between the struts which protrude
into the stent lumen in regions of curvature, thereby reducing flow
through the stent lumen. The walls of relatively long curved
vessels will not be well supported by Z-segments due to separation
of the stent struts at the greater curvature of the vessel.
[0092] The longitudinal flexibility of a stent, the radial force
distribution over the length of a stent, and the resistance to
kinking of a stent, are all also influenced by the geometry of the
closed-cell and Z-rings themselves. Referring to FIG. 3, the radial
forces exerted by an expanded stent portion formed of either
closed-cell segments or Z-segments increase as the angle between
two intersecting struts 1 defining a peak P(c) or P(z) of a
closed-cell ring or Z-ring of the fully expanded stein increases.
On the other hand, as the angle increases, it becomes more
difficult to collapse the stent into its unexpanded configuration
after manufacture in preparation for pre-loading and delivery of
the stent using a catheter system. The angle a is preferably in the
range of between 35.degree. to 65.degree., depending on the
diameter of the stent in its expanded configuration, the desired
radial force, the number of peaks in each annular ring, and the
thickness of the struts.
[0093] Referring to FIG. 4, the distance d between longitudinally
adjacent distal and proximate peaks P(z)d, P(c)d; P(z)p, P(c)p of
two adjacent annular rings also affects both flexibility and kink
resistance of a stent portion which includes those annular rings.
Specifically, increasing the distance d will increase the
longitudinal flexibility of the stent while decreasing the stent's
resistance to kinking. The distance d should be sufficiently great
to prevent any significant overlapping of adjacent struts when the
stent is bent and, at the same time, small enough to provide the
necessary vessel wall support in large curvature portions.
[0094] The shape, length, width and spacing of the interconnectors
interconnecting longitudinally adjacent Z-rings to form a
Z-segment, as well as interconnecting longitudinally adjacent
Z-rings and closed-cell rings, discussed below, all affect the
flexibility, kink resistance and radial force of stent portions
including those interconnected rings. Moreover, the degree to which
the stent foreshortens upon expansion from its unexpanded to its
expanded configuration is also affected by the geometric
characteristics of the interconnectors. Referring to FIG. 5(a),
adjacent distal and proximal Z-rings 100d and 100p are
longitudinally aligned and the distal peaks P(z)d of the proximal
Z-ring 100p are situated in aligned facing relationship to the
proximal peaks P(z)p of the distal Z-ring 100d. Longitudinally
extending linear interconnectors having a width equal to or
somewhat greater than the width of the struts 1, interconnect every
third pair of aligned facing peaks P(z)d, P(z)p to form a two-ring
Z-segment. Generally, increasing the length of the interconnectors
`I`, increases the flexibility of the segment, decreases the radial
force provided by the segment and decreases the kink resistance of
the segment. Generally, increasing the width of the interconnectors
Ta decreases the flexibility of the stent portion, increases the
kink resistance of the stent portion and does not materially affect
the radial force of the stent portion, compared to thinner
interconnectors of the same length. Increasing the spacing between
circumferentially adjacent interconnectors T., such as to every
fourth pair of aligned peaks from every third shown in FIG. 5(a),
generally increases the flexibility of the stent portion but
decreases the kink resistance, while the radial force remains about
the same.
[0095] Referring to FIG. 5(b), longitudinally aligned proximal and
distal Z-rings 100p and 100d are interconnected to form a Z-segment
by longitudinal linear interconnectors Tb which interconnect every
third pair of aligned valleys V(z)d, and V(z)p. Stent portions
incorporating Z-rings interconnected in this manner exhibit less
foreshortening upon expansion than stent portions incorporating
Z-rings interconnected as shown in FIG. 5(a). The other
characteristics of the stent portions remain about the same.
[0096] Referring to FIG. 5(c), longitudinally offset proximal and
distal Z-rings 100p and 100d are interconnected by linear,
longitudinal interconnectors I', that interconnect every third pair
of opposed peaks and valleys P(Z)d, and V(z)p of Z-rings 100p and
100d. A stent portion incorporating annular rings interconnected in
the manner of FIG. 5(c) has good flexibility and improved support
and coverage of vessel walls at areas of curvature. It will also
exhibit decreased foreshortening on expansion.
[0097] Referring to FIG. 5(d), the longitudinally offset proximal
and distal Z-rings 100p, 100d are interconnected by linear
interconnectors Td that extend obliquely between every third distal
peak P(z)d of proximal Z-ring 100p and an offset facing proximal
peak P(z)p of distal Z-ring 100d. Stent portions incorporating
Z-rings of this type exhibit greater flexibility than, for example,
stent portions incorporating Z-rings interconnected in the manner
shown in FIG. 5(a).
[0098] Referring to FIG. 5(e), the longitudinally aligned proximal
and distal Z-rings 100p and 100d are interconnected by
serpentine-shaped interconnectors T. which interconnect every third
pair of aligned peaks P(z)p, and P(z)d of distal and proximal
Z-rings 100d and 100p. Stent portions incorporating Z-rings
interconnected in this manner exhibit less foreshortening upon
expansion than in the case of FIG. 5(a).
[0099] Referring to FIG. 5(f), two longitudinally aligned Z-rings
1004 and 100p are interconnected by interconnectors Tf, which
connect every third pair of aligned peaks P(z)d, P(z)p. Each
interconnector Tf comprises a pair of outwardly bowed struts. Stent
portions incorporating Z-rings interconnected in this manner
exhibit a lesser degree of foreshortening than in the case of FIG.
5(a).
[0100] Referring to FIG. 5(g), two longitudinally aligned Z-rings
100p and 100d are interconnected by linear, longitudinal
interconnectors Tg which interconnect every third pair of opposed
peaks P(z)d, and P(z)p. However, unlike the construction of the
interconnectors T. of FIG. 5(a), each interconnector Tg has a width
of about twice the width of the struts 1 forming the Z-rings.
Increasing the thickness of the interconnectors Tg has the effect
of simplifying the process for manufacturing stents including such
interconnected Z-rings.
[0101] Referring to FIG. 6, a hexagonal-type closed-cell ring 200
is shown formed of a distal Z-ring 100d interconnected to an
aligned proximal Z-ring 100p by interconnectors T having a width of
about twice the thickness of the struts 1 defining the peaks P(c)p,
P(c)d. The increased width of the interconnectors T serves to
simplify the manufacturing process of stents incorporating
closed-cell rings constructed in this manner.
[0102] The manner in which adjacent closed-cell rings are
interconnected in closed-cell segments affects the characteristics
of stent portions incorporating those segments in much the same way
as the manner in which Z-rings are interconnected affects the
characteristics of stent portions incorporating those segments.
Referring to FIG. 7, two longitudinally aligned closed-cell rings
200d and 200p are interconnected by longitudinally extending linear
interconnectors T which interconnect every third pair of aligned
peaks P(c)p, and P(c)d_The configuration, length, width and spacing
of the interconnectors T can be varied in a manner analogous to
that discussed above in connection with the interconnection of
Z-rings with generally similar effects on the properties of the
stent portions incorporating those interconnected rings.
[0103] Referring to FIGS. 8(a) through 8(c), examples of pairs of
adjacent, longitudinally offset closed-cell annular rings 200d and
200p, interconnected by shared walls or struts 1a, are shown. In
particular, FIG. 8(a) illustrates a pair of longitudinally offset
proximal and distal closed-cell rings 200p and 200d having
hexagonal type closed-cell elements C are interconnected by shared
walls or struts 1a. The pairs of Z-rings forming each closed-cell
ring are interconnected by wavy-shaped interconnectors 179.
Interconnecting offset closed-cell rings 200d, 200p using shared
walls 1a, rather than linear interconnectors, such as
interconnectors T in FIG. 7, has the effect of increasing the
radial force, increasing the kink resistance and decreasing the
flexibility of a stent portion incorporating such interconnected
closed-cell rings. Utilizing a wavy-shaped interconnector 179 has
the effect of decreasing foreshortening upon expansion. FIG. 8(b)
shows a pair of longitudinally offset closed-cell rings 200d and
200p interconnected by shared walls or struts 1a. All of the struts
1, 1a have a wavy configuration which increases the flexibility of
a stent portion incorporating such interconnected closed-cell
rings. Referring to FIG. 8(c), a pair of longitudinally adjacent
offset closed-cell annular rings 200p and 200d is shown which are
interconnected by shared walls 1a and in which each of the
closed-cell elements C has a diamond shape, which makes the
closed-cell segment somewhat shorter, compared to FIGS. 8(a) and
8(b) and provides relative decrease in flexibility and increase in
kink resistance.
[0104] Referring to FIG. 9, a stent module 10 in accordance with
the invention is shown in its expanded configuration, cut
longitudinally and flattened. The module 10 can constitute an
entire scent or can be interconnected to other modules so as to
define an axial length portion of a modular stent incorporating
several stent modules.
[0105] Stent module 10 is formed of an intermediate Z-segment 12z
and distal and proximal closed-cell segments 14c and 16c
interconnected to the axial ends of Z-segment 12z. A module of this
type, i.e., including an intermediate Z-segment and a pair of
closed-cell end segments, i.e., a "C-Z-C" type module, is
designated a Type A module. The stent module 10 is the most simple
in construction of Type A stent modules in that each of the three
segments comprise only a single annular ring. Specifically, the
intermediate Z-segment 12z is formed of a single annular Z-ring 18z
having twelve distal peaks P(z)d and twelve proximal peaks P(z)p:
The distal closed-cell segment 14c is formed of a single
closed-cell annular ring 20c of the hexagonal type shown in FIG.
2(a) having twelve distal peaks P(c)d and twelve proximal peaks
P(c)p. The proximal closed-cell segment 16c is formed of a single
hexagonal-type closed-cell annular ring 22c having twelve distal
peaks P(c)d and twelve proximal peaks P(c)p.
[0106] In stent module 10, the pairs of longitudinally adjacent
annular rings, namely, rings 20c and 18z, and rings 18z and 22c,
are longitudinally aligned with respect to each other, i.e. their
opposed peaks P(c)d, P(z)d; P(z)p; P(c)d are longitudinally aligned
with each other. Specifically, the twelve proximal peaks P(c)p of
closed-cell ring 20c are longitudinally aligned with the twelve
distal peaks P(z)d of Z-ring 18z. Similarly the twelve distal peaks
P(c)d of closed-cell ring 22c are longitudinally aligned with the
twelve proximal peaks P(z)p of Z-ring 18z.
[0107] The intermediate Z-ring 18z is interconnected to each of the
distal and proximal closed-cell rings 20c, 22c by four
longitudinally extending linear interconnectors, Td and Tp
respectively, of the type shown in FIG. 5(a), interconnecting every
third pair of opposed peaks of the pairs of adjacent annular rings.
The interconnector elements Tp interconnecting the proximal side of
the intermediate Z-ring 18z to the distal side of annular
closed-cell ring 22c are situated circumferentially midway between
each adjacent pair of interconnector elements Td interconnecting
the distal side of the intermediate Z-ring 18z to the proximal side
of the distal annular closed-cell ring 20c. The uniform spacing of
the interconnector elements facilitates a uniform expansion of a
stent incorporating module 10.
[0108] A stent constructed from a plurality of interconnected
modules 10 will provide a high degree of radial force along
relatively long axial length portions, and relatively low
flexibility and kink resistance along its length due to the
repetition of closed-cell segments comprising pairs of
longitudinally adjacent closed-cell rings (at the connected ends of
adjacent modules) separated by Z-segments of only single Z-rings.
Such a stent is useful in treating a relatively long stenosis in a
relatively straight, or only somewhat curved, vessel. The use of
linear interconnectors Tp and Td in the manner shown and described
provides the stent with some degree of flexibility and uniform
expansion characteristics.
[0109] A stent constructed from a plurality of interconnected Type
A modules in general will provide good radial force distribution
over the length of the stent while the flexibility of the stent can
be increased by adding additional Z-rings to Z-segments of the
modules.
[0110] It will be understood that a module of the type shown in
FIG. 9 can be constructed with closed-cell rings having
configurations other than the type shown in FIG. 2(a), namely, with
one of the closed-cell ring types shown in FIGS. 2(b)-2(1), in
which case the specific above-discussed features associated with
such configuration will be obtained. Similarly, the manner of
interconnection between adjacent rings can be of any of the types
shown in FIGS. 5(a)-5(g), 6, 7 and 8(a)-8(c), in which case the
specific above-discussed features associated with such
interconnectors will be obtained.
[0111] Moreover, the manner of interconnection between adjacent
rings of two interconnected modules 10 can be varied. For example,
referring to FIG. 13, an axial length portion 60 of a stent is
illustrated formed of two interconnected Type A modules, 10d and
10p, each having the construction of module 10 shown in FIG. 9. In
this embodiment the proximal closed-cell ring 62c of the distal
module 10d and the distal closed-cell ring 64c of proximal module
10p are interconnected by shared walls or struts 1a of closed-cell
rings 62c, 64c. Alternatively, referring to FIG. 14, another axial
length portion 66 of a stent is illustrated formed of two Type A
modules 10d and 10p, each having the construction of module 10
shown in FIGS. 9 and 13. In this case, the proximal closed-cell
ring 68c of the distal module 10d and the distal closed-cell ring
69c of the proximal module 10p are interconnected by means of four
linear interconnectors T interconnecting opposed peaks P(c)p and
P(c)d of rings 68c and 69c, respectively, spaced at every third
pair of opposed peaks. The axial stent length portion 60 shown in
FIG. 13 has less flexibility than the axial stent length portion 66
shown in FIG. 14 in view of the shared wall interconnection of the
modules in the case of the former and the use of linear
interconnectors T in the case of the latter, so that the axial
stent length portion 66 shown in FIG. 14 is indicated for use where
there is a sharper bend in the vessel, i.e. the vessel segment has
a shorter radius of curvature.
[0112] Referring to FIG. 10, a stent module 24 in accordance with
the invention is formed of an intermediate closed-cell segment 26c
and distal and proximal Z-segments 28z and 30z interconnected to
the axial ends of closed-cell segment 26c. A module of this type,
i.e. including an intermediate closed-cell segment and a pair of
end Z-segments, i.e., a "Z-C-Z" type module, is designated a Type B
module.
[0113] The stent module 24 is the most simple in construction of
Type B stent modules in that each of the three segments comprise
only a single annular ring. Specifically, the intermediate
closed-cell segment 26c is formed of a single annular closed-cell
ring 32c of the hexagonal type shown in FIG. 2(a) having twelve
distal peaks P(c)d and twelve proximal peaks P(c)p. The distal
Z-segment 28z is formed of a single annular Z-ring 34z having
twelve distal and proximal peaks P(z)d, P(z)p. The proximal
Z-segment 30z is formed of a single annular Z-ring 36z having
twelve distal peaks P(z)d and twelve proximal peaks P(z)p.
[0114] Like module 10 of FIG. 9, the longitudinally adjacent rings
of module 24 are mutually positioned with their opposed peaks in
longitudinal alignment and the intermediate closed-cell ring 32c
interconnected to each of the distal and proximal Z-rings 34z, 36z
by four longitudinally extending linear interconnectors Td, Tp, of
the type shown in FIG. 5(a), respectively, interconnecting every
third pair of opposed peaks of the adjacent annular rings. The
interconnectors Tp interconnecting the proximal side of the
intermediate closed-cell ring 32c to the proximal Z-ring 36z are
situated circumferentially midway between each adjacent pair of
interconnectors Td interconnecting the distal side of the
intermediate closed-cell ring 32c to the distal Z-ring 34z in order
to facilitate a uniform expansion of a stent incorporating module
24.
[0115] A stent constructed from a plurality of modules 24, unlike a
stent formed from a plurality of modules 10 (FIG. 9), will provide
a high degree of radial force along relatively short axial length
portions, and relatively high flexibility and kink resistance along
its length, due to the repetition of Z-segments coMprising pairs of
longitudinally adjacent Z-rings (at the connected ends of adjacent
modules) separated by closed-cell segments, each only of a single
closed-cell ring. Such a stent is useful in treating a relatively
short stenosis situated at or near the apex of a substantially
curved vessel or in a tortuous vessel. The use of linear
interconnector elements Tp and Td in the manner shown and described
provides the stent with additional flexibility and uniform
expansion characteristics. As in the case of module 10, the
particular configuration of the closed-cell rings and the specific
manner of interconnection between longitudinally adjacent rings can
be varied from that shown in FIG. 10.
[0116] A stent constructed from a plurality of interconnected Type
B module in general will have good flexibility along its length
while the length of the stent providing a high radial force can be
increased by adding additional closed-cell rings to closed-cell
segments of the modules.
[0117] Referring to FIG. 11, a Type A stent module 40 similar to
the Type A module 10 shown in FIG. 9 is illustrated. Stent module
40 differs from module 10 in that each of the annular rings,
namely, intermediate Z-ring 42z and distal and proximal closed-cell
rings 44c and 46c, define sixteen distal and proximal peaks P(c)d,
P(c)p., P(z)d, P(z)p; P(c)d, P(c)p. Opposed, longitudinally aligned
peaks P(z)d, P(c)p, of adjacent rings 42z and 44c are
interconnected by four longitudinally extending linear
interconnectors Td interconnecting every fourth pair of opposed
peaks while longitudinally aligned peaks P(z)p, P(c)d of adjacent
rings 42z and 46c are interconnected by four longitudinally
extending linear interconnectors Tp interconnecting every fourth
pair of opposed peaks. If the length of the struts 1 forming the
Z-rings and closed-cell rings of the module 40, and the angle a at
the bends of Z-rings and closed-cells, are the same as the length
of the struts 1 and angles forming the rings of module 10, the
diameter of a stent incorporating module 40 will be greater than
the diameter of a stent incorporating module 10. On the other hand,
if the length of struts 1 forming the rings of module 40 is reduced
with a constant angle at the bends, or if the length of the struts
1 is the same, but the angle of the bends is reduced, compared to
module 10, so that the diameter of the stent incorporating module
40 will be the same as the diameter of a stent incorporating module
10, an axial portion of a stent incorporating module 40 will
provide an increased coverage or scaffolding, i.e. an increased
metal to vessel wall ratio, compared to an axial portion of a stent
incorporating module 10.
[0118] Likewise, the Type B stent module 50 shown in FIG. 12 is
similar to the Type B module 24 shown in FIG. 10, differing only in
the number of peaks defined by the annular rings (16 versus 12) and
the spacing of the interconnectors (every fourth pair versus every
third pair). In the case where the struts 1 of stent module 50 are
the same length as the struts 1 of stent module 24 (FIG. 10), and
the angle at the bends is also the same as in stent module 24, the
diameter of the axial stent portion incorporating module 50 will be
greater than the diameter of a stent portion incorporating module
24 whereas if the struts are shorter with the constant angle, or if
the struts are the same, but the angles reduced, compared to module
24, the metal to vessel wall ratio is increased.
[0119] Referring to FIG. 15, a stent 70 in accordance with the
present invention is illustrated comprising three stent modules,
namely, an intermediate Type B module 72i and distal and proximal
Type A end modules 74d and 76p. The stent and its modales are
formed of annular rings, each having twelve distal and proximal
peaks, which are longitudinally aligned with the distal and
proximal peaks of longitudinally adjacent annular rings
interconnected by linear interconnectors T situated at every third
pair of aligned peaks.
[0120] The intermediate Type B module 72i of stent 70 comprises an
intermediate closed-cell segment 78c consisting of a single
closed-cell ring 80c, distal and proximal Z-segments 82z and 84z,
the distal Z-segment 82z consisting of four Z-rings 85z and the
proximal Z-segment 84z consisting of four Z-rings 87z.
[0121] The distal Type A module 74d comprises an intermediate
Z-segment 86z consisting of four Z-rings 88z and a pair of distal
and proximal closed-cell end segments 89c and 90c, each consisting
of a single closed-cell ring 92c. Similarly, the proximal Type A
module 76p comprises an intermediate Z-segment 94z consisting of
four Z-rings 96z and a pair of distal and proximal closed-cell end
segments 98c and 99s each consisting of a single closed-celling
97c.
[0122] The stent 70 has good flexibility and kink resistance and is
particularly useful for long irregular lesions situated in a curved
vessel. The relatively long Z-segments 82z, 84z, 86z and 94z, each
comprising four Z-rings, provide good flexibility along the entire
length of the stent, while the closed-cell segments 78c, 89c, 90c,
98c and 99c, each constituted by a single closed-cell ring, provide
high radial force and good kink resistance along uniformly spaced
intervals of the length of the stent 70. The provision of a single
closed-cell ring 80c at the center and more peripheral closed-cell
rings 92c and 97c of the stent provide good kink resistance when
the stent is bent at these segments through small radius curved
vessels.
[0123] Referring now to FIGS. 16-18, a stent 300 in accordance with
the invention is illustrated which is capable of treating a wide
variety of lesions, and which provides good wall apposition in
tortuous vessels and superior resistance to kinking when situated
in vessels having acute bends.
[0124] The stent 300 comprises three stent modules, namely, an
intermediate Type B module 302i, and distal and proximal Type A end
modules 304d and 306p. The intermediate module 302i includes an
intermediate closed-cell segment 308c constituted by a single
closed-cell ring 310c, and distal and proximal Z-segments 309z and
311z, the distal Z-segment 309z consisting of two Z-rings 314z and
the proximal Z-segment 311z consisting of two Z-rings 313z.
[0125] The distal Type A module 304d comprises an intermediate
Z-segment 316z consisting of three Z-rings 318z and distal and
proximal closed-cell end segments 320c and 322c, each of which
consists of a single closed-cell ring 324c and 326c respectively.
Similarly, the proximal Type A module 306p comprises an
intermediate Z-segment 328z consisting of three Z-rings 330z and
distal and proximal closed-cell segments 332c and 334c, each of
which consists of a single closed-cell ring 336c and 338c.
[0126] The annular rings forming stent 300 each define twelve
distal and proximal peaks, and the rings are arranged with their
opposed peaks in longitudinal alignment with each other. The rings
are interconnected by linear interconnectors T extending between
every third pair of opposed peaks.
[0127] The closed-cell rings are of the hexagonal cell type shown
in FIG. 2(a) but it is understood that other closed-cell ring
configurations may be used to obtain the particular characteristics
associated with those configurations as discussed above. In this
connection, it is noted that the most distal and proximal rings of
stent 300, namely, closed-cell rings 324c and 338c are elongated
compared to the other closed-cell rings of stent 300. In other
words, the interconnectors Tc interconnecting the Z-ring components
forming the closed-cell rings 324c and 338c are longer than the
interconnectors T interconnecting the rings of the remainder of the
stent. By this construction, the distal and proximal closed-cell
rings provide a greater stability at the ends of the stent for
better anchoring and improved stabilization of the stent in the
vessel: It is understood that the end closed cells do not
necessarily have to be different in size, compared to other
closed-cell segments within the same stent. For example, referring
to FIG. 16, the end closed-cells 324c and 338c can be the same in
size as closed-cells 326c, 310c and 336c.
[0128] With reference to FIG. 17, it is common for lesions to be
located in curved vessel segments which can be extremely tortuous
thereby requiring the stent to provide additional features specific
to such applications. In this connection, a common and significant
problem in the case where a lesion is located at or near a small
radius curved vessel segment arises from a decrease of wall
coverage and radial force of struts of Z-rings of conventional
stents in the region of the curvature. At the same time, an
additional problem arises in the region of the inner vessel
curvature where the struts of Z-rings of conventional stents
overlap each other. Referring to FIG. 17, by providing the
intermediate module 302i as a Type B module with only a single
closed-cell ring 310c constituting the intermediate module segment,
and a pair of Z-segments, each consisting of two Z-rings 313z, 314;
adjacent to the closed-cell ring the stent can be bent up to
180.degree. with the region of the apex of the stent providing good
vessel wall coverage and higher radial force. With this
construction, the overlap of adjacent struts in the inner region of
the apex of curvature of the stent is also reduced. Moreover, this
construction provides good wall support in areas of the vessel
adjacent to the apex of curvature in cases where the stenosis is
not at the region of curvature but close to it by virtue of
closed-cell rings 326c and 336c. Thus, despite the accentuated
acute angle, the overall integrity of the inner stent lumen is
preserved, with relatively little effect on wall coverage, radial
force and strut overlap.
[0129] Further, referring to FIG. 18, the stent 300 is shown
positioned in an S-shaped moderately tortuous vessel 340. The close
apposition of the stent 300 to the vessel wall 342 along the
tortuous vessel segment, which is provided by the particular
"A-B-A" modular construction, and the high degree of flexibility
inherent therein, is illustrated.
[0130] It is also possible to form the stents of the invention in a
tapered configuration, such as for use in a narrowing vessel, by
expanding the small diameter tubes on tapered mandrels. For
example, referring to FIG. 27, a tapered stent 300T is illustrated
having the same sequence and configuration of closed-cell rings and
Z-rings as stent 300 of FIG. 16.
[0131] Referring to FIG. 19, a laser-slotted tube 344 is shown
which constitutes a stent similar in configuration to stent 300,
but with the end closed-cells identical in size to the central
closed-cells, and shown in its unexpanded configuration, cut
longitudinally and flattened. The tube 344 is constructed of a very
thin cylinder of nickel-titanium alloy approximately 0.15-0.30 mm
in thickness. The tube is about 1.6-1.8 mm in diameter. A computer
controlled laser beam cuts a series of slots S through the tube 344
as well as cutout regions R cooperating with the slots to define
the struts 1 and interconnectors T. In manufacture, the tube 344 is
progressively expanded by fitting it over mandrels of progressively
increasing diameters so that the struts circumferentially open at
their points of intersection to define the peaks and valleys. The
stent is heat treated after each expansion to impart to it the
desired temperature sensitive memory characteristics, with the
final expansion and heat treatment step determining the final
diameter of the stent in its expanded configuration. In the case of
the laser-slotted tube 344, the tube is expanded from 1.8 mm to 12
mm in several steps. Any one of the intermediate steps can be a
final step if a smaller final stent diameter is indicated for a
particular application.
[0132] The tube 344 has a length of about 6 cm, although it is
understood that the tube can be cut to any desired length. With a
length of 6 cm, the stent can be used in treating a stenosis up to
about 4 cm in length, in which case the stenosis should be centered
along the length of the stent so that the ends of the stent,
including closed-cell rings 324c and 338c, appose healthy regions
of the vessel wall to anchor the stent in place.
[0133] The five closed-cell segments 320c, 322c, 308c, 332c and
334c spaced at intervals over the length of the stent provide a
relatively uniform high radial force distribution over the length
of the stent so that the stent can be used to treat from very short
to very long stenoses with assurance that a high radial force will
be applied by the stent. At the same time, the four Z-segments
316z, 309z, 311z and 328z situated between the closed-cell segments
provide good flexibility along the length of the stent to enable
the stent to be used in tortuous vessels as shown in FIG. 18. The
particular numbers of closed-cell rings and Z-rings in each
closed-cell and Z-segment of stent are chosen in this embodiment to
provide uniform, high radial force distribution and flexibility for
a large variety of types and lengths of stenoses and a high degree
of longitudinal flexibility, both in its unexpanded configuration
shown in FIG. 19 as well as in its expanded configuration shown in
FIG. 18. Moreover, the provision of the three central single-ring
closed-cell segments 326c, 310c and 336c, each of which is bounded
on its distal and proximal ends by Z-segments incorporating two or
more Z-rings, provides the stent with good kink resistance
characteristics along its length. As seen in FIG. 17, which shows
the stent 300 bent about 180.degree. at its central region, the
single closed-cell ring 310c will provide good radial support at
the apex of the bend, while the struts of the closed-rings 313z,
313z, 314z, 314z only slightly overlap thereby allowing the stent
lumen to remain open for flow. Similar resistance to kinking will
be obtained if stent 300 is bent at its end regions proximate to
single-ring closed-cell segments 326c and 336c.
[0134] Referring to FIG. 20, a stent module 400 according to the
invention is illustrated, cut longitudinally and flattened,
particularly suitable for use in a stent for a vessel in which a
lesion is situated at or near a side branch to that vessel. The
module 400 comprises a Type A module including an intermediate
Z-segment 402z consisting of eight Z-rings 404z and distal and
proximal closed-cell end segments 406d and 408p, each consisting of
a single closed-cell ring 410c and 412c respectively. A relatively
large irregular diamond-shaped cell or window 414 is formed
centrally in the intermediate Z-segment 402, having a length
extending over six Z-rings and a width extending at its widest
point over four Z-ring peaks, through which the end of another
stent situated in the side branch to the vessel can be received.
The four corners of the window 414 are coated with radio-opaque
material 416 in order to assist the clinician in accurately
positioning the stent so that the window is situated at the side
branch.
[0135] The stents according to the invention can be formed of thin,
porous fenestrated micro-tube elements of the type schematically
shown in FIG. 21. The porous nature of micro-tube element 418 is
schematically indicated at 420. The stent tube elements are filled
with medication, usually in gel form, prior to delivery so that
once the stent is delivered and expanded, the medication will
gradually release, shown schematically at 422, into the blood
stream or into the vessel wall for treatment of a particular
condition, or to prevent restenosis at the site of stent
deployment.
[0136] Referring to FIG. 22, another preferred embodiment of a
stent, designated 500, in accordance with the present invention is
shown in its expanded configuration, cut longitudinally and
flattened. Stent 500 exhibits minimal foreshortening upon expansion
and provides high radial strength at its closed-cell segments and a
high degree of flexibility at its Z-segments.
[0137] Stent 500 comprises an intermediate Type B module 502i
interconnected at its distal and proximal ends to Type B end
modules 504d and 506p. Intermediate module 502i comprises an
intermediate closed-cell segment 508c consisting of a single
closed-cell ring 510c, a distal Z-segment 512z consisting of a
single Z-ring 514z and a proximal Z-segment 516z consisting of a
single Z-ring 518z. Closed-cell ring 510c is of the type shown in
FIG. 2(d) thereby providing this portion of the stent with reduced
foreshortening characteristics with only slightly less radial force
and flexibility than closed-cell rings of the type shown in FIG.
2(a). The distal and proximal Z-rings 514z, 518z are longitudinally
offset with respect to intermediate closed-cell ring 510c and are
interconnected to the closed-cell ring 510c by interconnectors Tc
in accordance with the arrangement shown in FIG. 5(c).
[0138] The distal end module 504d comprises an intermediate
closed-cell segment 520c consisting of a single closed-cell ring
522c, again of the FIG. 2(d) type, a distal Z-segment 524z
consisting of four Z-rings 526z interconnected to each other and to
closed-cell ring 522c by interconnectors Tc, again in accordance
with the FIG. 5(c) arrangement, and a proximal Z-segment 528z
consisting of a single Z-ring 530z. The closed-cell ring 522c is
interconnected to the Z-ring 530z by interconnectors T. of the type
shown in FIG. 5(a). The proximal end module 506p is essentially a
mirror-image of the distal end module 504d.
[0139] By using closed-cell rings of the FIG. 2(d) type in all
three modules and interconnectors To of the FIG. 5(c) type, the
stent 500 will exhibit a minimum degree of foreshortening upon
expansion and relative high radial strength along the length of the
stent. The long Z-segments of the distal and proximal end modules
504d, 506p, comprising four Z-rings, provide the stent with good
flexibility at its ends. Reduced foreshortening of the stent upon
expansion allows a more accurate positioning of the stent at the
desired location of the vessel.
[0140] Referring to FIG. 23; another preferred embodiment of a
stent, designated 600, in accordance with the present invention is
shown in its expanded configuration, cut longitudinally and
flattened. Like stent 500, stent 600 will exhibit a minimum degree
of foreshortening upon expansion.
[0141] Stent 600 comprises an intermediate Type B module 602i
interconnected at its distal and proximal ends to Type A end
modules 604d and 606p. Intermediate module 602i comprises an
intermediate closed-cell segment 608c consisting of a single
closed-cell ring 610c, a distal Z-segment 612z consisting of two
Z-rings 614z and a proximal Z-segment 616z consisting of two
Z-rings 618z. As in the case of stent 500, closed-cell ring 610c is
of the FIG. 2(d) type providing reduced foreshortening
characteristics. The proximal and distal Z-rings 614z, 618z are
interconnected to the intermediate closed-cell ring 610c by
interconnectors To of the FIG. 5(c) type.
[0142] The distal end module 604d comprises an intermediate
Z-segment 620z consisting of two Z-rings 622z interconnected by
FIG. 5(c) type interconnectors T., separated by four pairs of
opposed peaks and valleys, a distal closed-cell segment 624c
consisting of a single closed-cell ring 626c of the FIG. 2(d) type
and connected to the adjacent Z-ring 622z by FIG. 5(a) type
interconnectors T., and a proximal closed-cell segment 628c
consisting of a single closed-cell ring 630c of the FIG. 2(d) type
and connected to the adjacent Z-ring 622z by a FIG. 5(c) type
interconnector T. The proximal end module 606, is essentially a
mirror image of the distal end module 604d. The stent 600 also
exhibits minimum foreshortening upon expansion due to the
combination of the FIG. 5(a) and FIG. 5(c) type interconnectors and
FIG. 2(d) type closed-cell rings.
[0143] Referring now to FIGS. 24(a) and 24(b), as non-uniform,
multi-segment stents are manufactured from thinner laser-slotted
tubes with narrower struts, problems may arise with achieving
geometric regularity in the stent construction in its expanded
configuration.
[0144] Specifically, an end portion of a small diameter
laser-slotted tube 700 formed of a nickel-titanium alloy for
producing a self-expandable stent is shown in FIG. 24(a), cut
longitudinally and flattened. The end portion of the laser-slotted
tube embodies a stent module 710 including an intermediate
Z-segment 712z consisting of two Z-rings 714z interconnected by
interconnectors T1 and distal and proximal closed-cell segments
716c and 718c consisting of single dosed-cell rings 720c and 722c
respectively which are connected to Z-rings 714z by interconnectors
T2.
[0145] In the manufacture of a self-expanding stent, slots S and
cutout regions R are initially cut in the tube 700 by a laser beam
to define the struts and interconnectors. The tube is then
progressively mechanically expanded and heat treated in several
steps, such as by applying the slotted tube over mandrels of
progressively increasing diameter, until the tube is expanded to
its final diameter. In this connection, the tube 700 in this
embodiment having an initial diameter of 1.8 mm can be mechanically
expanded in progressive steps to different final diameters, e.g., 6
mm, 8 mm or 12 mm, depending upon the actual application to which
the stent will be put.
[0146] Referring to FIG. 24(b), when the stent is formed with
annular rings of different geometry, e.g. Z-rings and closed-cell
rings 720c, 714z, 722c, and, especially when the tube 700 is formed
of thin material, e.g. 0.16-0.22 mm, and the struts 1 formed by the
slots S are narrow, e.g., less than about 0.2 mm, the stent will
tend to expand during manufacture in an irregular manner, i.e. with
the cells of each closed-cell ring and the Z-shaped portions of
each Z-ring having an irregular or distorted geometry. This is due
to some struts being situated closer to interconnectors than others
and being constrained against movement to a. greater extent than
those struts situated further from those regions. For example,
referring to FIG. 24(b) which illustrates the stent module 710
expanded to a diameter of 6 mm, the closed-cells A, B, C and D in
closed-cell rings 720c and 722c, the peaks of which are connected
to the Z-rings 714z by interconnectors T2, are circumferentially
wider than the other closed-cells in those rings. Similarly, the
configuration of the Z-shaped portions of Z-rings 714z are
irregular and distorted around the circumference of each of the
Z-rings. If those geometric irregularities remain in the final
stent, which is likely in the case of stents having relatively
small final diameters, the stent will not provide uniform radial
force and will not provide good wall apposition, as well as uniform
metal-to-Wall ratio circumferentially, with larger cells allowing
protrusion of atherosclerotic material into the vessel lumen.
[0147] Referring to FIG. 25(a) in which the end portion 810 of a
laser-slotted small diameter tube 800 is shown, this problem is
overcome by laser-cutting the small diameter tube 800 to define a
plurality of longitudinally adjacent Z-rings 812z, 814z, 816z,
818z, 820z, 822z, each Z-ring having a plurality of peaks and
valleys, and providing temporary and permanent interconnector
portions, Tt and Tp, integrally joining adjacent pairs of Z-rings
so that every pair of adjacent Z-rings constitutes, at least
temporarily, a closed-cell ring. Thus, adjacent Z-rings 812z and
814z constitute a closed-cell ring 830c, adjacent Z-rings 814z and
816z constitute a closed-cell ring 832c, adjacent rings 816z and
818z constitute a closed-cell ring 834c, adjacent rings 818z and
820c constitute a closed-cell ring 836c and adjacent rings 820z and
822z constitute a closed-cell ring 838c.
[0148] The small diameter tube is then expanded and heat treated to
its final diameter as seen in FIG. 25(c) whereupon the temporary
interconnectors TT are removed from the expanded tube (FIG. 25(d)),
either mechanically or by laser-cutting, to provide the desired
sequence and arrangement of closed-cell and Z-rings, namely 830c,
816z, 818z, 838c. The expanded tube is then electro-polished to
smoothen all surfaces. Each of the closed-cell rings and Z-rings
has a regular, non-distorted configuration since the temporary
interconnectors TT functioned to constrain the opposed peaks of
adjacent annular rings to remain in uniform regular relationship
during the expansion step.
[0149] As best seen in FIG. 25(b), the temporary interconnectors TT
of tube 800 constitute thin webs of tube material integrally
joining pre-shaped peaks P(z)p, P(z)d of adjacent Z-rings, e.g.
Z-rings 814z and 816z. Each permanent interconnector Tp essentially
constitutes a continuation of a respective pair of struts forming
the opposed peaks of adjacent Z-rings which remain interconnected
after expansion of the tube and removal of the temporary
interconnectors Tp. Thus, as seen in FIG. 25(c), after the tube 800
has been expanded, the temporary struts TT are significantly
thinner than the permanent struts Tp and are easily identified for
mechanical removal.
[0150] The temporary interconnectors TT can have other forms than
that shown in FIGS. 25(a) and 25(b). For example, as shown in FIG.
25(e), in order to facilitate manual removal, the temporary
interconnectors TT can be formed in the tube 800 to include
enlarged flag portions 850 joined to respective opposed aligned
peaks P(z)d and P(z)p by very short, thin connecting portions 852a
and 852b. These enlarged flag portions are easily grasped by a tool
to facilitate removal after the tube has been expanded to its final
diameter.
[0151] Another problem may arise in the manufacture of stents from
laser-slotted tubes, whether of the self-expanding or
balloon-expandable type, when the tubes are formed of very thin
material and it is desired to provide wider struts to increase the
metal to wall ratio of the stent.
[0152] Specifically, referring to FIG. 26(a), a portion of a
laser-slotted metallic tube 900 is shown in which the struts 1 are
formed between slots S and regions R from which the tube material
is removed. The slots S define the width of the struts 1 and have
conventionally been a certain minimum thickness Ts for the reason
that as the tube 900 is expanded and the struts diverge from each
other about their intersection points defined by the ends of each
slot S, the tube material at the inner region V of the vertex of
pairs of intersecting struts is placed under high stress and will
tear if the width of the slot Tdot is too small. However,
increasing the width of the laser beam and width of the slots 'Lid
will result in the struts 1 having a reduced thickness T1 and may
not provide the desired metal to wall ratio and radial force.
[0153] Referring to FIG. 26(b), according to the invention, the
width T810 of slots S can be maintained small, e.g. to 20 microns,
by providing enlarged radius openings 902, e.g. where the radius of
the openings 902 is 60-80 microns, at the end of each slot. The
enlarged radius openings 902 act as stress relievers as the tube
900 is expanded and the struts diverge at the end of each slot to
form the peaks. By enabling the slots S to be narrower, the width
Tit of struts 1 can be increased, enabling a better metal to wall
ratio for the stent, higher radial force and improved kink
resistance. This will also improve the process of expanding the
stent, resulting in a more ilniform cell geometry throughout the
stent.
[0154] Referring now to FIGS. 28-30, it is often costly and
time-consuming to create specific software for guiding the
laser-cutting tool to cut a particular desired sequence and
arrangement of closed-cell rings and Z-rings in a small diameter
tube to provide a stent with optimal characteristics for a
particular clinical application. In accordance with the invention,
stent blanks are initially prepared, which may be done before
particular clinical application of the stent is known, and
therefore before the desired sequence and arrangement of the
Z-rings and closed-cell rings has been determined, from which a
stent having any desired sequence and arrangement can be simply and
quickly made. Thus, a manufacturer may maintain an inventory of
stent blanks so that when a patient requires a stent for a
particular application, e.g., for use in a tortuous vessel where
the stenosis is situated in a small radius curved portion, a
clinician can request a stent having the sequence and configuration
of Z-rings and closed-cell rings particularly suited for that
application, which can be simply and quickly made from one of the
stent blanks, loaded into the delivery system, sterilized and
shipped to the hospital.
[0155] In accordance with the invention, a stent blank is formed by
laser-cutting a small diameter tube to define a plurality of
longitudinally adjacent Z-rings having interconnector portions
integrally joining adjacent Z-rings in a manner such that every
pair of adjacent Z-rings constitutes a closed-cell ring. The small
diameter tube is then expanded and heat-treated to form the stent
blank. Once the particular desired sequence and arrangement of
closed-cell rings and Z-rings is determined, certain interconnector
portions are removed from the blank, either mechanically or by
laser, to provide the desired stent configuration.
[0156] Referring to FIG. 28(a), a stent blank 80 manufactured by
expanding and heat treating a small diameter tube of shape-memory
material is shown. The blank 80 is formed of a plurality of Z-rings
82 situated in aligned relationship with each other with each pair
of proximate aligned peaks P(z) being interconnected by
interconnector portions T, so that every pair of adjacent Z-rings
82 forms a closed-cell ring 84 in the manner described in
connection with FIG. 2(a). Closed-cell rings 84 are interconnected
by shared walls in the manner described in connection with FIG.
8.
[0157] Stents having a wide variety of sequences and arrangements
Of closed-cell rings and Z-rings suitable for different clinical
applications can be made simply and quickly from blanks 80. For
example, where a stenosis requires a uniform radial force
distribution along an extended length, the practitioner may
determine that a stent having the following sequence of closed-cell
rings and Z-rings will be optimal: CCZZC ZZCZZ MCC, where C
designates a close-cell ring and Z designates a Z-ring.
[0158] Referring to FIG. 28(b), a blank 80 is quickly and simply
processed to form a stent 85 having this configuration by removing
selected interconnector portions T from between selected pairs of
adjacent Z-rings. For example, beginning at the distal end of stent
85, closed-cell rings 84a and 84b are "formed" having the
configuration and properties of closed-cell ring 200a in FIG. 2(a)
by leaving, i.e. not removing, the interconnectors Ta, Th that join
every pair of proximate aligned peaks of adjacent pairs of Z-rings
821, 822 and 822 823. The Z-ring 823 is formed having the
configuration and properties of the Z-rings 100 shown in FIG. 5(a)
by removing pairs of interconnectors Tc joining circumferentially
adjacent pairs of proximate aligned peaks, i.e. leaving the
interconnectors Tc that join every third pair of proximate aligned
peaks of adjacent Z-ring pair 823, 824. The formation of the
remainder of stent. 85 is apparent from the foregoing.
[0159] Not only can any desired sequence of closed-cell rings and
Z-rings be obtained using the blank 80, but the arrangement of each
ring itself can be varied. For example, the closed-cell ring 84a
can be formed by removing the interconnectors Ta joining every
other pair of proximate aligned peaks so that the closed-cell ring
will have the configuration and properties of closed-cell 200b
shown and described in FIG. 2(b).
[0160] FIG. 28(c) illustrates a stent 85 made from the stent blank
90 having the following sequence of closed-cell. rings and Z-rings:
ZZZCZZ ZCCCZ ZZCZZZ, which may be desired where a high radial force
is needed along a relatively short length of a tortutous
vessel.
[0161] FIG. 29(a) illustrates another stent blank 87 in accordance
with the invention. The stent blank 87 comprises a plurality of
Z-rings 88 situated in aligned relationship to each other with
interconnectors T joining every pair of proximate aligned valleys
to form closed-cell rings 89, each having the configuration and
properties of the closed-cell ring 200c of FIG. 29(c). Stents
formed from blank 87 generally will exhibit a lesser degree of
foreshortening upon expansion than stents formed from blank 80 of
FIG. 28(a).
[0162] FIG. 29(b) illustrates a stent 90 made by removing
appropriate interconnectors from the stent blank 87 and having the
following sequence of closed-cell rings and Z-rings: CCZZZC ZCZ
CZZZCC, which may be desired for certain applications apparent from
the foregoing. In this case, closed-cell rings are formed by
leaving interconnectors T joining every pair of proximate aligned
valleys of adjacent Z-rings while Z-rings are formed by removing
interconnectors T joining circumferentially adjacent pairs of
proximate aligned valleys, i.e., leaving the interconnectors T that
join every third pair of proximate aligned valleys.
[0163] FIG. 29(c) illustrates a stent 91 made by removing
appropriate interconnectors from the stent blank 87 and having the
following sequence of closed-cell rings and Z-rings: CC7ZZC ZCZ
CZZZCC which may be desired for certain applications apparent from
the foregoing. It is noteworthy that some of the closed-cell rings
C, e.g. ring C1, of stent 91 are formed by leaving interconnectors
T joining every pair of proximate aligned valleys, while other
closed-cell rings C, e.g. ring C2, of stent 91, are formed by
removing interconnectors T from every other pair of proximate
aligned valleys.
[0164] FIG. 29(d) illustrates a stent 91A made from stent blank 87
and having the following sequence of closed-cell rings and Z-rings:
ZZZCZ ZZCCCZZ ZCZZZ.
[0165] FIG. 30(a) illustrates a third stent blank 93 in accordance
with the invention. The stent blank 93 comprises a plurality of
Z-rings 94 situated in offset relationship to each other (except
for Z-rings 94. and 94b which are in alignment with each other),
with interconnectors T joining every proximate aligned peak and
valley pair to form closed-cell rings 95, each having the
configuration and properties of the closed-cell ring 200e or 200h
of FIGS. 2(e) and 2(h). Closed-cell rings 94a and 941) and
interconnectors Ta from a closed-cell ring 95a having the
configuration and properties of the closed-cell ring 200c of FIG.
29(c). Stents formed from blank 93 generally will exhibit a lesser
degree of foreshortening, but similar flexibility and kink
resistance compared to stents formed from blank 80.
[0166] FIG. 30(b) illustrates a stent 96 made by removing
appropriate interconnectors from the stent blank 93 having the
following sequence of closed-cell rings and Z-rings: CZZZC ZZCZZ
CZ77C. Similarly, FIG. 30(c) illustrates another stent 97 made from
stent blank 93 having the following sequence of closed-cell rings
and Z-rings: ZZZCCZZ ZCZ ZZCCZZZ.
[0167] It is also within the scope of the invention to form a stent
blank, prior to determining the sequence and arrangement of the
closed-cell rings and Z-rings, from an enlarged diameter tube by
laser-cutting the enlarged diameter tube to define a plurality of
longitudinally adjacent Z-rings which are interconnected by
interconnector portions such that every pair of adjacent Z-rings
constitutes a closed-cell ring. Once the particular sequence and
configuration of the closed-cell rings and Z-rings has been
determined, appropriate interconnector portions are removed as in
the previously disclosed methods.
[0168] Obviously, numerous modifications and variations of the
present invention are possible in the light of the above teachings.
It is therefore to be understood that within the scope of the
claims, the invention may be varied from what is specifically
disclosed herein.
* * * * *